Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation

Xi, Weixian; Peng, Haiyan; Aguirre‐Soto, Alan; Kloxin, Christopher J.; Stansbury, J.W.; Bowman, Christopher N.

doi:10.1021/ma501366f

Cited by 130 publications

(137 citation statements)

References 51 publications

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“…The quantum yield obtained is analogous to the value reported by Xi and co-workers ( ϕ chem = 0.15) for the same photocaged superbase catalyst, although the authors used a different experimental setup and calculation method. 29 Since optically thin samples are simulated and were tested experimentally, both the photobase concentration and UV-light irradiance are presumed to be independent of film thickness.…”

Section: Theoretical Model Developmentmentioning

confidence: 99%

“…PBG’s, such as 2-(2-nitrophenyl)propyloxycarbonyl-1,1,3,3-tetramethylguanidine (NPPOC-TMG) and coumarin-TMG, have also shown to exhibit very low basicity when the base is under protection and remain relatively stable within formulated monomer mixtures, but once photocleaved led to a dramatic increase in basicity of the released organobase, allowing the reaction to proceed in a living fashion even at extremely low amounts of the free TMG. 29,30 …”

Section: Introductionmentioning

confidence: 99%

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Mechanistic Kinetic Modeling of Thiol–Michael Addition Photopolymerizations via Photocaged “Superbase” Generators: An Analytical Approach

et al. 2016

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A kinetic mechanism and the accompanying mathematical framework are presented for base-mediated thiol–Michael photopolymerization kinetics involving a photobase generator. Here, model kinetic predictions demonstrate excellent agreement with a representative experimental system composed of 2-(2-nitrophenyl)propyloxycarbonyl-1,1,3,3-tetramethylguanidine (NPPOC-TMG) as a photobase generator that is used to initiate thiol–vinyl sulfone Michael addition reactions and polymerizations. Modeling equations derived from a basic mechanistic scheme indicate overall polymerization rates that follow a pseudo-first-order kinetic process in the base and coreactant concentrations, controlled by the ratio of the propagation to chain-transfer kinetic parameters (kp/kCT) which is dictated by the rate-limiting step and controls the time necessary to reach gelation. Gelation occurs earlier as the kp/kCT ratio reaches a critical value, wherefrom gel times become nearly independent of kp/kCT. The theoretical approach allowed determining the effect of induction time on the reaction kinetics due to initial acid–base neutralization for the photogenerated base caused by the presence of protic contaminants. Such inhibition kinetics may be challenging for reaction systems that require high curing rates but are relevant for chemical systems that need to remain kinetically dormant until activated although at the ultimate cost of lower polymerization rates. The pure step-growth character of this living polymerization and the exhibited kinetics provide unique potential for extended dark-cure reactions and uniform material properties. The general kinetic model is applicable to photobase initiators where photolysis follows a unimolecular cleavage process releasing a strong base catalyst without cogeneration of intermediate radical species.

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Section: Theoretical Model Developmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanistic Kinetic Modeling of Thiol–Michael Addition Photopolymerizations via Photocaged “Superbase” Generators: An Analytical Approach

et al. 2016

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“…In the CuAAC reaction, the copper(I) catalyst is typically introduced by the in situ reduction of copper(II) into copper(I) 4,5 or by the direct addition of copper(I) salt in the presence of a base which immediately triggers the azide–alkyne cycloaddition reaction 6,7 . Despite its utility in applications requiring bio-orthogonal reactions 8,9 , the CuAAC reaction had previously lacked the temporal control characteristic of other photo-enabled click reactions, such as the thiol-ene 10 and thiol-yne 11,12 radical mediated reactions as well as the photocaged-base-thiol-Michael addition 13 .…”

Section: Introductionmentioning

confidence: 99%

Towards understanding the kinetic behaviour and limitations in photo-induced copper(i) catalyzed azide–alkyne cycloaddition (CuAAC) reactions

El-Zaatari

Shete

Adzima

et al. 2016

Phys. Chem. Chem. Phys.

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The kinetic behaviour of the photo-induced copper(I) catalyzed azide—alkyne cycloaddition (CuAAC) reaction was studied in detail using real-time Fourier Transform Infrared Spectroscopy (FTIR) on both a solvent-based monofunctional and a neat polymer network forming system. The results in the solvent-based system showed near first-order kinetics on copper and photoinitiator concentrations up to a threshold value in which the kinetics switch to zeroth-order. This kinetic shift shows that the photo-CuAAC reaction is not suseptible from side reactions such as copper disproportionation, copper(I) reduction, and radical termination at the early stages of the reaction. The overall reaction rate and conversion is highly dependent on the initial concentrations of photoinitiator and copper(II), as well as their relative ratios. The conversion was decreased when an excess of photoinitiator was utilized compared to its threshold value. Interestingly, the reaction showed an induction period at relatively low intensities. The induction period is decreased by increasing light intensity, and photoinitiator concentration. The reaction trends and limitations were further observed in a solventless polymer network forming system, exhibiting a similar copper and photoinitiator threshold behaviour.

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“…We recently used this method for the calculation of quantum yields of photolysis of photobase generators. 62 When using polychromatic light sources, I abs is most often not accounted for because it requires full-spectrum integration in the UV−vis region where absorbance and emission overlap. Thus, I abs determination has been mostly limited to cases in which monochromatic laser irradiation is used to trigger the polymerization reaction because one-wavelength activation solely requires knowledge of the initial concentration of the light-absorbing initiator and the molar absorptivity at single emission wavelength (ε) as well as the path length of the sample.…”

Section: Resultsmentioning

confidence: 99%

Coupled UV–Vis/FT–NIR Spectroscopy for Kinetic Analysis of Multiple Reaction Steps in Polymerizations

et al. 2015

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We couple UV−vis and FT−NIR spectroscopy for the real-time monitoring of polymerization reactions, allowing the simultaneous tracking of the rates of light absorption and initiator/monomer consumption, from which dynamic and previously difficult-to-measure parameters are calculated: quantum yields of initiator consumption, initiation and polymerization, photosensitivity, and residual content of leachable chromophore. Estimating these parameters from one set of experiments is not possible with any other probing technique. We demonstrate the potential of this technique using the free radical initiating system including camphorquinone as photoreducible chromophore and amines as reductants for the visible-light-triggered bulk polymerization of methacrylate monomers, important for dental and biomaterials. Photoinitiation by camphorquinone/amine pairs in two dimethacrylates serves to show the importance of obtaining quantum yields in the polymerizing medium instead of using inert solvents. Additionally, the often-intricate interactions between initiation reactions and the developing macromolecular architectures can be elucidated. For instance, we present the quantification of fluctuations in quantum yields as a function of polymerization. This robust analytical tool with up to millisecond resolution opens opportunities in gaining mechanistic insights from the myriad of macromolecular syntheses available to date.

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Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation

Cited by 130 publications

References 51 publications

Mechanistic Kinetic Modeling of Thiol–Michael Addition Photopolymerizations via Photocaged “Superbase” Generators: An Analytical Approach

Mechanistic Kinetic Modeling of Thiol–Michael Addition Photopolymerizations via Photocaged “Superbase” Generators: An Analytical Approach

Towards understanding the kinetic behaviour and limitations in photo-induced copper(i) catalyzed azide–alkyne cycloaddition (CuAAC) reactions

Coupled UV–Vis/FT–NIR Spectroscopy for Kinetic Analysis of Multiple Reaction Steps in Polymerizations

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